Rework and add some features

[valflrt]

• Added more particle types but now they are called "particle classes"
• Make it possible to move around and zoom in/out
• Improved efficiency by using array2d instead of array of Vec
• Separate ui and simulation threads for more flexible (or not ?) simulation. A system of events has been established to share content between the ui and simulation threads.
• Kind of improved ui (it's subjective)
• Also added interesting seeds (ignore them)

The calculations for one frame take around 30ms for 4000 particles and 40ms for 5000 particles (on my average laptop).

august 2024 edit: I added spatial partitioning which allows running similations with thousands (up to 120000) with an acceptable update rate (rarely above 50-80ms)